In recent years, a surface acoustic wave (hereinafter, “SAW”) device is widely used in a field of mobile communications, and it is often used for portable phones or the like especially because of its excellent features such as high performance, size reduction, and mass productivity. Along with generalization of small size packaging called CSP (Chip Size Package) in semiconductor parts, a resin sealing method utilizing the CSP technique is introduced in view of facilitation of reduction in the device size and an improvement in productivity according to a batch type manufacturing method in the SAW device.
As a SAW device utilizing the CSP technique, there are structures disclosed in JP-A No. 2002-184884, JP-A No. 2002-217219, JP-A No. 2002-217220, and JP-A No. 2002-314234 (hereinafter, these structures are called “conventional technology 1”). FIG. 10 illustrates a structure of the CSP type SAW device disclosed in the conventional technology 1. The SAW device shown in FIG. 10 includes a SAW chip 103 having an IDT for oscillating a SAW and electrode pads arranged on a main face 103a of a piezoelectric substrate positioned on a lower side in FIG. 10, and a mounting substrate 101 having connection pads 102 arranged on a main face 101a positioned on an upper side in FIG. 10. The electrode pads provided on the lower face of the SAW chip 103 and the connection pads 102 provided on the mounting substrate 101 are conductively fixed to each other via metal bumps 104, and a main face 103b of the SAW chip 103 positioned on an upper side in FIG. 10 and side faces thereof are covered with a resin sheet 105 such that the main face 103b comes in close contact with the side faces so that an airtight space 106 is formed between the face 103a and the face 101a. 
A method for manufacturing the SAW device will be explained below. After the SAW chip 103 and the mounting substrate 101 are flip-chip mounted, the resin sheet 105 is placed on the SAW chip 103, and the resin sheet is heated up to a resin softening temperature, so that the resin sheet 105 is deformed to come in close contact with the surface of the SAW chip 103 and the mounting substrate 101 in conformity with contours thereof. After the resin sheet 105 is deformed, further heating is conducted to impart fluidablility to the resin sheet 105, so that the resin sheet is caused to adhere to the SAW chip 103 and the mounting substrate 101, and the shape of the resin sheet 105 is fixed by curing the resin sheet. A shrinking force is generated when the resin sheet 105 is cured, so that it serves to press the SAW chip 103 toward the mounting substrate 101. Thus, the resin sheet 105 is brought in close contact with the SAW chip 103 and the mounting substrate 101 more tightly. In the conventional technology, since the shape of the resin sheet 105 can easily be deformed to conform with an outer face of the SAW chip, the SAW chip can be sealed without affecting operation of the SAW chip.
In the conventional technology 1, however, since an area of the upper face of the SAW chip 103 is small relative to the mounting substrate 101, it is difficult to effect marking for filter identification and conduct sucking for device pickup, and there is a problem of fragility, poor moisture resistance, or the like due to a structure in which the thin resin sheet 105 is merely brought in close contact with the SAW chip 103 in conformity with the outer face thereof. Further, since the resin sheet 105 is brought in close contact with the SAW chip 103 by applying a temperature gradient to the resin sheet 105 to generate shrinking force in the resin sheet, corners A at the SAW chip 103 become thin, so that the SAW chip 103 may be exposed externally, which may deteriorate the quality of the SAW chip 103.
Furthermore, another example of a manufacturing method is disclosed in JP-A No. 2002-217218 (hereinafter, “conventional technology 2”). As shown in FIG. 11, in the method, a resin sheet 105 is brought in close contact with an inner wall 200a tightly to deform the resin sheet 105 by providing a jig 200 with a shape conforming with a contour of a SAW chip 103 and sucking air through a hole 201a of a suction pipe 201. Thereafter, the jig 200 is disposed on the SAW chip 103 and the resin sheet 105 is caused to adhere to the SAW chip 103 and the mounting substrate 101 such that the resin sheet 105 is brought in close contact with surfaces of the SAW chip 103 and the mounting substrate 101, while the resin sheet 105 is heated. In the conventional technology 2, since the shape of the resin sheet 105 is deformed in advance so as to conform with surface shapes of the SAW chip 103 and the mounting substrate 101 by the jig 200, the SAW chip and the mounting substrate can be covered securely.
In the conventional technology 2, since the resin is brought in close contact with the SAW chip after the shape of the resin is deformed, a possibility that corners on an upper face of the SAW chip are exposed is reduced. However, the problem of fragility, poor moisture resistance, or the like due to thinness of the resin film and other problems of difficulties in working for marking or device pickup can not be addressed like the conventional technology 1. Furthermore, since resin sealing is performed using the jig, it is necessary to prepare jigs corresponding to respective sizes of the SAW chips, which deteriorates the working efficiency.
Furthermore, as another conventional technology, there is a structure disclosed in JP-A No. 2002-334954 (hereinafter, “conventional technology 3”). This structure corresponds to a structure in which an electrically conductive film layer is further formed on the resin sheet 105 in the structure of the SAW device shown in FIG. 10. In the conventional technology 3, since the electrically conductive film layer is formed on the resin, the moisture resistance is improved, but the problems as in the conventional technologies 1 and 2 such that the resin sheet is fragile due to its thinness and difficulties in working for marking and device pickup are not yet solved.
The present invention has been achieved in order to solve the above problems, and an object thereof is to provide a method for manufacturing a SAW device in which a SAW chip is flip-chip mounted on a mounting substrate and surfaces of the SAW chip and the mounting substrate are sealed with resin, wherein the SAW chip is firmly protected and quality of the SAW device is improved.